1. Field of the Invention
The present invention relates to a light-projecting/receiving unit equipped with a scanning system; and, in particular, to an omnidirectional distance detecting apparatus, equipped with such a light-projecting/receiving unit, capable of detecting over 360 degrees therearound whether an object exists or not, the distance to the object, and the angle to the object.
2. Related Background Art
A distance detecting apparatus having a light projector using a laser, light-emitting diode, or the like for generating irradiation light to be emitted outside and a light receiver using a photodiode for detecting reflected light from an object and detects whether the object exists in a detecting direction or not and the distance to the object from the time difference between the light projection and light reception or the like has conventionally been known as a distance sensor system mounted in an automatic guided vehicle, for example.
The detecting direction in such an apparatus is the direction in which the irradiation light is projected outside and the reflected light from the outside is received. The detecting direction can be selected if the optical path of the irradiation light emitted from the light projector and the optical path of the reflected light made incident on the light receiver are changed to a predetermined direction by reflecting means such as a reflecting mirror which is optical path changing means. Here, the optical path changing means may be configured so as to be secured to and installed in a rotary mechanism which is rotatable by a predetermined rotary shaft, such that the detecting direction can be changed continuously, and the sidewall of surroundings of the optical path changing means being rotated may be configured optically open to the outside, such that the detecting direction can be rotated and changed substantially over 360 degrees therearound. As a consequence, an omnidirectional type distance detecting apparatus which can detect the distance to the object in all directions can be attained.
In an omnidirectional distance detecting apparatus such as the one mentioned above, the position of detected object can be specified if not only the distance to the object based on the light projection and reception but also the angle (direction) to the object is detected. Namely, while whether an object exists or not is detected according to whether reflected light is received from the object or not, if the reflected light is received, so that the object exists, then the distance to the object is detected according to the time difference between light projection and light reception or the like, and the angle to the object is detected by angle detection means, such as transmission type optical encoder, installed with respect to the rotary mechanism such that the angle of rotation in the detecting direction can be measured. Examples of such apparatus include those disclosed in Japanese Patent Application Laid-Open No. HEI 7-191142 and No. HEI 10-10233.
In the above-mentioned conventional omnidirectional distance detecting apparatus, while the optical path changing means is fixed onto a rotary shaft, the light projector and light receiver are disposed opposite each other on the rotary shaft so as to face their respective predetermined reflecting surfaces of the optical path changing means. Namely, the light projector is disposed at one end part of the rotary shaft, so as to emit irradiation light along the rotary shaft, and the optical path thereof is changed by optical path changing means, such as light projection mirror, to a detecting direction which is perpendicular to the rotary shaft, so that the light is emitted outside. On the other hand, the light receiver is disposed at the other end part of the rotary shaft, such that the optical path of the reflected light from the object incident in the detecting direction is changed by optical path changing means, such as light-receiving mirror, to a direction extending along the rotary shaft, whereby the light is incident on the light receiver.
Thus configured apparatus has been problematic in that, since the light projector and light receiver are installed at substantially both ends of the rotary shaft, i.e., both ends of the apparatus, a wire such as signal line becomes longer and limits the degree of freedom in designing the rotary mechanism and the like. Also, since this line is required to pass through a region where the projection of irradiation light to the outside and the reception of reflected light from the outside are carried out, complete 360-degree omnidirectional distance detection has been impossible. Further, such a longwire enhances the influence of electric noise from the rotary driving system of rotary mechanism and the like, thereby causing the accuracy of distance detection to deteriorate.
In view of the problems mentioned above, it is an object of the present invention to provide an omnidirectional distance detecting apparatus which enables distance detection over 360 degrees with a high accuracy.
For achieving such an object, the present invention provides an omnidirectional distance detecting apparatus, comprising a light projector and a light receiver within a housing, for emitting irradiation light from the light projector to a predetermined detecting direction outside the housing by way of projecting light optical path changing means and causing reflected light from an object in the detecting direction to be made incident on the light receiver by way of receiving light optical path changing means, so as to detect whether the object exists or not and a distance to the object; the apparatus comprising a rotary mechanism having a rotating part installed so as to be rotatable about a predetermined axis within the housing as an axis of rotation and a rotary driving part for driving the rotating part, the projecting light optical path changing means and receiving light optical path changing means being secured and installed on the axis of rotation; angle detection means for detecting an angle of rotation of the rotating part; and a signal processing circuit for detecting the distance to the object according to a signal from the light projector and light receiver and an angle to the object according to a signal from the angle detection means; a region within the housing being divided along the direction of axis of rotation into an optical system region and a driving system region within which the light projector, light receiver, and signal processing circuit are disposed, a side wall of the optical system region being constituted by a transparent tube transparent to light; the optical system region being further divided along the direction of axis of rotation into a light-projecting region, including the projecting light optical path changing means therein, for emitting the irradiation light into the detecting direction; and a light-receiving region adjacent the driving system region, including the receiving light optical path changing means therein, for receiving the reflected light from the detecting direction; the light-projecting region and light-receiving region being optically separated from each other by light-shielding means, installed so as to be fixed with respect to the transparent tube, for blocking stray light deviating from an optical path; the light receiver having irradiation light guiding means, disposed on the axis of rotation so as to oppose the receiving light optical path changing means and installed within the light-projecting region, for guiding the irradiation light from the light projector to the projecting light optical path changing means.
The present invention also provides an omnidirectional distance detecting apparatus, comprising a light projector and a light receiver within a housing, for emitting irradiation light from the light projector to a predetermined detecting direction outside the housing by way of projecting light optical path changing means and causing reflected light from an object in the detecting direction to be made incident on the light receiver by way of receiving light optical path changing means, so as to detect whether the object exists or not and a distance to the object; the apparatus comprising a rotary mechanism having a rotating part installed so as to be rotatable about a predetermined axis within the housing as an axis of rotation and a rotary driving part for driving the rotating part, the projecting light optical path changing means and receiving light optical path changing means being secured and installed on the axis of rotation; angle detection means for detecting an angle of rotation of the rotating part; and a signal processing circuit for detecting the distance to the object according to a signal from the light projector and light receiver and an angle to the object according to a signal from the angle detection means; a region within the housing being divided along the direction of axis of rotation into an optical system region and a driving system region within which the light projector, light receiver, and signal processing circuit are disposed, a side wall of the optical system region being constituted by a transparent tube transparent to light; the optical system region being further divided along the direction of axis of rotation into a light-projecting region adjacent the driving system region, including the projecting light optical path changing means therein, for emitting the irradiation light into the detecting direction; and a light-receiving region, including the receiving light optical path changing means therein, for receiving the reflected light from the detecting direction; the light-projecting region and light-receiving region being optically separated from each other by light-shielding means, installed so as to be fixed with respect to the transparent tube, for blocking stray light deviating from an optical path; the light projector being disposed on the axis of rotation so as to oppose the projecting light optical path changing means; the omnidirectional distance detecting apparatus having reflected light guiding means, installed within the light-receiving region, for guiding the reflected light from the receiving light optical path changing means to the light receiver.
In the configurations mentioned above, both the light projector and light receiver are installed in the driving system region located on the same side of the projecting light optical path changing means and receiving light optical path changing means, which are optical path changing means, with respect to the direction along the axis of rotation of the rotary mechanism. As a consequence, wires such as signal lines within the optical system region including the light-projecting region and light-receiving region can be eliminated, so as to enable complete 360-degree omnidirectional distance detection, and the degree of freedom in design and the like are secured so as to enhance the functionality of apparatus, whereas the wiring to the signal processing circuit can be shortened, so as to reduce the influence of electric noise on light-receiving signals and the like, thereby restraining the accuracy in distance detection from deteriorating.
In such an apparatus configuration, it is necessary that at least one of light projector and light receiver be disposed at a position deviating from the axis of rotation of the rotary mechanism. In this case, it is necessary to provide irradiation light guiding means for guiding the irradiation light from the light projector or reflected light guiding means for guiding the reflected light to the light receiver.
Namely, while the light projector is disposed at a position deviating from the axis of rotation in the case where the light receiver is disposed on the axis of rotation, light can be projected and received in a configuration comprising irradiation light guiding means, such as reflecting prism, for guiding the irradiation light from the light projector to the projecting light optical path changing means as mentioned above.
In the case where the light receiver is disposed at a position deviating from the axis of rotation while the light projector is disposed on the axis of rotation, light can be projected and received in a configuration comprising reflected light guiding means, such as reflecting prism, for guiding the reflected light from the receiving light optical path changing means to the light receiver.
The angle detection means may comprise an angle detection disk, secured to an outer periphery of the rotating part, having an angle detection slit group constituted by a plurality of slits disposed at equally spaced intervals on a predetermined circle centered at the axis of rotation; a photoelectric unit for photoelectrically detecting passage through the slits; a clock circuit for generating an electric signal in a high-speed pulse form having a predetermined frequency; and angle calculating means for calculating the angle to the object by using the detection of slits obtained by the photoelectric unit and the number of pulses of electric signal caused by the clock circuit.
Though the angle to the object can be detected by a transmission type optical encoder having a disk and a photoelectric unit in an apparatus such as the one mentioned above, the angular resolution is determined by the slit arrangement interval in the angle detection slit group, whereby the angle cannot be detected with a high resolution in this case. If angle detection by means of an electric signal with a high-speed pulse is employed together therewith, by contrast, then angle can be detected with a high resolution without changing the slit arrangement interval.
Though both the light projector and light receiver are installed in the driving system region located on the same side of the projecting light optical path changing means and receiving light optical path changing means, which are optical path changing means, with respect to the direction along the axis of rotation of the rotary mechanism, whereby wires such as signal lines within the optical system region including the light-projecting region and light-receiving region are eliminated, so as to enable complete 360-degree omnidirectional distance detection in the above-mentioned apparatus, an optical axis structure in which the light exit position and light entrance position coincide with each other may be considered in the light souce and photodetector employed in the omnidirectional distance detecting apparatus.
If a drop of water or the like attaches onto the light exit position of the transparent tube in such a case, however, then diffuse reflection may also occur at the time when light is incident thereon, thereby enhancing the error in detection. For suppressing such an error in detection, the present invention provides a light-projecting/receiving unit for emitting light outside from within a transparent tube by way of a light exit position on the transparent tube, and causing a reflected part of the light from the outside to enter the transmission tube byway of a light entrance position on the transparent tube; wherein the light-projecting/receiving unit comprises a light source and a photodetector which are disposed so as to correspond to the light exit and light entrance positions, respectively, such that the light exit and light entrance positions are positions different from each other on the transparent tube; a light-shielding barrier provided in the transparent tube so as to separate the light exit and light entrance positions from each other; and a scanning optical system, disposed on a path of the light emitted from the light source and on a path of the light incident on the photodetector, for moving the light exit and light entrance positions.
Here, the transparent tube is a tube transparent to the light emitted from the light source and the light incident on the photodetector, and refers to a tube transparent in the visible range when these kinds of light are visible light, though it may be opaque in the visible range as long as it is transparent in the infrared range if these kinds of light are infrared rays, for example.
While the light exit and entrance positions are scanned with the scanning optical system in this unit, even when a drop of water or the like is attached to the transparent tube, its diffuse reflection can be suppressed, and the light-shielding barrier suppresses the diffuse reflection occurring at one of the positions, whereby optical scanning can be carried out with a high accuracy.
Preferably, the scanning optical system comprises first and second reflecting surfaces for reflecting the light from the light source to the light exit position and the light from the light entrance position to the photodetector, respectively, whereas the first and second reflecting surfaces are disposed on the center axis of the transparent tube and rotate about the center axis. Since the center axis becomes the center of rotation, this scanning optical system can carry out scanning without deflecting the optical path between each of light source and photodetector and its corresponding reflecting surface.